Mg-based bulk metallic glasses: Elastic properties and their correlations with toughness and glass transition temperature

In this work, elastic properties of Mg-based bulk metallic glasses (BMGs) with different chemical compositions were investigated. By compositional tuning in the quaternary Mg–Cu–Ag–Y alloys, the Poisson’s ratioνof 0.332 is achieved at Mg56Cu21Ag14Y9BMG, in excess of the previously suggested critical value (ν= 0.31–0.32) for the brittle-to-tough transition in metallic glasses. With the properties of the constituent elements, the predicted values of the bulk modulusBand shear modulusμof Mg-based BMGs are 8% and 10% greater than the measured value, respectively. Notch toughnessKQof the ten investigated Mg-based BMGs varies between 3.6 and 8.2 MPa√m. Intrinsic brittleness of Mg glass is associated with its tiny plastic zone size (in micrometer scale) and weak resistance to crack propagation. The toughness variations are lack of significant correlation with theνorμ. Among the investigated alloys, the Mg59.5Cu22.9Ag6.6Gd11BMG manifests a good combination of improved toughness and high glass-forming ability.